In Situ Shale Wettability Regulation Using Sophisticated Nanoemulsion to Maintain Wellbore Stability in Deep Well Drilling

Wettability alteration of the shale surface is a potential strategy to address wellbore instability issues arising from shale hydration. In this study, we have explored an oil-in-water (o/ w) nanoemulsion, in which soluble silicate (lithium silicate and potassium methyl silicate) as the aqueous phase and organosilanes (3-methacryloxypropyltrimethoxysilane (KH570) and n-octyltrie-thoxysilane (n-OTES)) as the oil phase, as a shale inhibitor via forming a hydrophobic artificial borehole shield in situ on shale surfaces to maintain wellbore stability in high-temperature drilling operations. The shale dispersion test showed the highest shale recovery of nanoemulsion was up to 106.4% compared to that of water (20%), and recovered shale cuttings remained at the original integrity after hot rolling at 180 degrees C, indicating superior inhibition performance and resistance to elevated temperatures. Moreover, recovered shale cuttings manifested water repellency upon reimmersion in water, ascribed to the hydrophobic film, preventing water from permeating into the shale. The results of the contact angle measurement elucidated that the film wettability, from hydrophilic to superhydrophobic (ranging from 9.6-154 degrees), can be achieved by altering the n-OTES-to-KH570 weight ratio from 0.2 to 2.25, and the film with the highest hydrophobicity (154 degrees) and the lowest surface energy (3.17 mJ center dot m-2) can be obtained at a ratio of 1.3. Scanning electron microscopy images demonstrated that the superhydrophobic film was composed of tightly stacked reticulate nanofilaments with a diameter of 7-17 nm and several micrometers in length and overlapped well-distributed nanospheres with a diameter of 30 nm. X-ray diffraction and Fourier transform infrared spectroscopy confirmed the film was crystalline silica grafted with long-chain alkylsiloxane. It is assumed that the unique micronanostructure combined with the siloxane modification contributed to the hydrophobicity. Consequently, this study provides a potential alternative solution for wellbore stabilization in deep well drilling engineering by employing nanoemulsion as a shale hydration inhibitor via forming a protective film with controllable wettability. Furthermore, it can be conferred a practical application due to easily available, less hazardous, and cost-effective materials.

Automated summary

In this study, an oil-in-water nanoemulsion was explored as a potential strategy for shale inhibition. The nanoemulsion formed a hydrophobic protective film on shale surfaces, which effectively maintained wellbore stability in high-temperature drilling operations. The results showed that the nanoemulsion had superior inhibition performance and resistance to elevated temperatures, and the shale surfaces treated with the nanoemulsion exhibited water repellency. The wettability of the film could be controlled by adjusting the ratio of different components in the nanoemulsion.